The invention relates to the use of alkylformamides to reduce the surface tension in water-based systems.
The ability to reduce the surface tension of water is of great importance in waterborne coatings, inks, adhesives, and agricultural formulations because decreased surface tension translates to enhanced substrate wetting in actual formulations. Surface tension reduction in water-based systems is generally achieved through the addition of surfactants. Performance attributes resulting from the addition of surfactants include enhanced surface coverage, fewer defects, and more uniform distribution. Equilibrium surface tension performance is important when the system is at rest. However, the ability to reduce surface tension under dynamic conditions is of great importance in applications where high surface creation rates are utilized. Such applications include spraying, rolling and brushing of coatings or spraying of agricultural formulations, or high speed gravure or ink-jet printing. Dynamic surface tension is a fundamental quantity which provides a measure of the ability of a surfactant to reduce surface tension and provide wetting under such high speed application conditions.
Traditional nonionic surfactants such as alkylphenol or alcohol ethoxylates, and ethylene oxide (EO)/propylene oxide (PO) copolymers have excellent equilibrium surface tension performance but are generally characterized as having poor dynamic surface tension reduction. In contrast, certain anionic surfactants such as sodium dialkyl sulfosuccinates can provide good dynamic results, but these are very foamy and impart water sensitivity to the finished coating.
There is a need for a family of surfactants which provide good equilibrium and dynamic surface tension properties, are low-foaming and would be widely accepted in the waterborne coating, ink, adhesive, and agricultural formulation industries.
The importance of reducing equilibrium and dynamic surface tension in applications such as coatings, inks, and agricultural formulations is well-appreciated in the art.
Low dynamic surface tension is of great importance in the application of waterborne coatings. In an article, Schwartz, J. xe2x80x9cThe Importance of Low Dynamic Surface Tension in Waterborne Coatingsxe2x80x9d, Journal of Coatings Technology, September 1992, there is a discussion of surface tension properties in waterborne coatings and a discussion of dynamic surface tension in such coatings. Equilibrium and dynamic surface tension were evaluated for several surface active agents. It is pointed out that low dynamic surface tension is an important factor in achieving superior film formation in waterborne coatings. Dynamic coating application methods require surfactants with low dynamic surface tensions in order to prevent defects such as retraction, craters, and foam.
Efficient application of agricultural products is also highly dependent on the dynamic surface tension properties of the formulation. In an article, Wirth, W.; Storp, S.; Jacobsen, W. xe2x80x9cMechanisms Controlling Leaf Retention of Agricultural Spray Solutionsxe2x80x9d; Pestic. Sci. 1991, 33, 411-420, the relationship between the dynamic surface tension of agricultural formulations and the ability of these formulations to be retained on a leaf was studied. These workers observed a good correlation between retention values and dynamic surface tension, with more effective retention of formulations exhibiting low dynamic surface tension.
Low dynamic surface tension is also important in high-speed printing as discussed in the article xe2x80x9cUsing Surfactants to Formulate VOC Compliant Waterbased Inksxe2x80x9d, Medina, S. W.; Sutovich, M. N. Am. Ink Maker 1994, 72 (2), 32-38. In this article, it is stated that equilibrium surface tensions (ESTs) are pertinent only to ink systems at rest. EST values, however, are not good indicators of performance in the dynamic, high speed printing environment under which the ink is used. Dynamic surface tension is a more appropriate property. This dynamic measurement is an indicator of the ability of the surfactant to migrate to a newly created ink/substrate interface to provide wetting during high speed printing.
U.S. Pat. No. 5,098,478 discloses water-based ink compositions comprising water, a pigment, a nonionic surfactant and a solubilizing agent for the nonionic surfactant. Dynamic surface tension in ink compositions for publication gravure printing must be reduced to a level of about 25 to 40 dynes/cm to assure that printability problems will not be encountered.
U.S. Pat. No. 5,562,762 discloses an aqueous jet ink of water, dissolved dyes and a tertiary amine having two polyethoxylate substituents and that low dynamic surface tension is important in ink jet printing.
Desando, et al; J. Chem Phys. 1983, 78, 3238-3244 examined the dielectric absorption properties of n-octylformamide in conjunction with a study of the surfactant properties of n-octyl ammonium formate in nonpolar matrices such as toluene and polystyrene.
EP 36560 A2 discloses N-(higher alkyl) C1-C8 amides as foam stabilizers in synthetic resin compositions.
Various long chain N-(sec-alkyl) formamides were used as intermediates for the preparation of derivatives of the corresponding N-(sec-alkyl) amines [Ishizuka et al, Chim. Phys. Appl. Prat. Ag. Surface, C. R. Cong. Int. Deterg., 5th 1969, Volume 1, pp 183-91]. Surface tension, wetting power, foaming power, and foam stability of the derivatives were studied, indicating they possess surfactant properties in aqueous media. No surfactant properties are noted for the formamides.
GB 1,357,372 discloses water-immiscible formamides as dispersion solvents for photographic color formers. Dibutylformamide and dibenzylformamide are noted as being particularly useful.
DE 4341986-A1 discloses a large number of carboxylic acid amides of the formula 
including those where R may be H and R1 and R2 may be hydrogen or alkyl as well as many other organic groups, as crystallization inhibitors in certain aqueous azole fungicide compositions. Compounds I-40 and I-41 are 2-ethylhexylformamide and n-octylformamide, respectively.
This invention provides water-based compositions containing an organic or inorganic compound, particularly aqueous organic coating, ink, and agricultural compositions, having reduced equilibrium and dynamic surface tension by incorporation of an effective amount of an alkylformamide compound of the following structure: 
where R is a C5 to C11 alkyl group, provided that the organic compound is not an azole derivative fungicide. It is desirable that an aqueous solution of the alkylformamide demonstrates a dynamic surface tension of less than 45 dynes/cm at a concentration of xe2x89xa65 wt % in water at 23xc2x0 C. and 1 bubble/second according to the maximum-bubble pressure method. The maximum-bubble-pressure method of measuring surface tension is described in Langmuir 1986, 2, 428-432, which is incorporated by reference.
Also provided is a method for lowering the equilibrium and dynamic surface tension of aqueous compositions by the incorporation of these alkylformamide compounds.
Also provided is a method for applying a water-based inorganic or organic compound-containing composition to a surface to partially or fully coat the surface with the water-based composition, the composition containing an effective amount of an alkylformamide compound of the above structure for reducing the dynamic surface tension of the water-based composition.
There are significant advantages associated with the use of these alkylformamides in water-based organic coatings, inks, and agricultural compositions and these advantages include:
an ability to formulate water-borne coatings, inks, and agricultural compositions which may be applied to a variety of substrates with excellent wetting of substrate surfaces including contaminated and low energy surfaces;
an ability to provide a reduction in coating or printing defects such as orange peel and flow/leveling deficiencies;
an ability to produce water-borne coatings and inks which have low volatile organic content, thus making these surfactants environmentally favorable; and
an ability to formulate coating and ink compositions capable of high speed application.
Because of their excellent surfactant properties and the ability to control foam, these materials are likely to find use in many applications in which reduction in dynamic and equilibrium surface tension and low foam are important. Applications in which low foam is important include various wet-processing textile operations, such as dyeing of fibers, fiber souring, and kier boiling, where low-foaming properties would be particularly advantageous; they may also have applicability in soaps, water-based perfumes, shampoos, and various detergents where their marked ability to lower surface tension while simultaneously producing substantially no foam would be highly desirable.
This invention relates to the use of compounds of the formula 
where R is a C5 to C11 alkyl group for the reduction of equilibrium and dynamic surface tension in water-based compositions containing an organic compound, particularly coating, ink, and agricultural compositions containing organic compounds such as polymeric resins, herbicides (excluding azole derivative fungicides), insecticides or plant growth modifying agents. It is desirable that an aqueous solution of the alkylformamide demonstrates a dynamic surface tension of less than 45 dynes/cm at a concentration of xe2x89xa65 wt % in water at 23xc2x0 C. and 1 bubble/second according to the maximum-bubble-pressure method. The maximum-bubble-pressure method of measuring surface tension is described in Langmuir 1986, 2, 428-432, which is incorporated by reference.
In one aspect of the invention the alkylformamides of the above formula display excellent ability to reduce equilibrium and dynamic surface tension while producing substantially no foam.
The compounds of the invention may be prepared by reacting a suitable amine with an alkylformate 
Alternatively, these compounds may be prepared by direct carbonylation of an amine in the presence of a suitable catalyst: 
Both of these methods are well-known in the art.
The alkyl group may be a linear, branched, or cyclic C5 to C11 hydrocarbon moiety. In general, lower numbers of alkyl carbon or a higher degree of branching will increase the solubility of the surfactant but decrease the efficiency (i.e. a greater amount will be required to obtain a given reduction in surface tension). The alkyl groups may be linear or branched and the point of attachment to nitrogen may be on either a terminal or internal carbon. Examples of suitable alkyl groups include 1-pentyl, 2-pentyl, 3-pentyl, 2-(3-methylbutyl), 2-(2-methylbutyl), 1-(3-methylbutyl), 1-(2-methylbutyl), 1-hexyl, 2-hexyl, 3-hexyl, cyclohexyl, 1-(4-methylpentyl), 1-(3-methylpentyl), 1-(2-methylpentyl), 2-(4-methylpentyl), 3-(3-methylbutyl), 1-heptyl, 2-heptyl, 3-heptyl, 1-(5-methylhexyl), 1-(4-methylhexyl), 2-(3-methylhexyl), 1-octyl, 2-ethylhexyl, 2-octyl, 3-octyl, isooctyl, cyclooctyl, n-nonyl, 2-nonyl, 3-nonyl, 4-nonyl, isononyl, n-decyl, isodecyl, 2-decyl, 3-decyl, n-undecyl, cycloundecyl, and the like. Of course, this list is not comprehensive, and the particular alkyl group chosen for a particular use will depend on the performance characteristics required for that application. Alkyl groups which comprise a mixture of isomers are also suitable for the practice of this invention. C6 to C8 hydrocarbon moieties are preferred and C8 hydrocarbon moieties are especially preferred.
The alkylformamides are suitable for use in an aqueous composition comprising in water an inorganic compound which is a mineral ore or a pigment or an organic compound which is a pigment, a polymerizable monomer, such as addition, condensation and vinyl monomers, an oligomeric resin, a polymeric resin, a detergent, a caustic cleaning agent, a herbicide, especially a herbicide for chlorophyll-containing plants, an insecticide, or a plant growth modifying agent.
An amount of the alkylformamide compound that is effective to reduce the equilibrium and/or dynamic surface tension of the water-based, organic or inorganic compound-containing composition is added. Such effective amount may range from 0.001 to 10 g/100 mL, preferably 0.01 to 1 g/100 mL, and most preferably 0.05 to 0.5 g/100 mL of the aqueous composition. Naturally, the most effective amount will depend on the particular application and the solubility of the particular alkylformamide.
In the following water-based organic coating, ink, and agricultural compositions containing an alkylformamide according to the invention, the other listed components of such compositions are those materials well known to the workers in the relevant art.
A typical water-based protective or decorative organic coating composition to which the alkylformamide surfactants of the invention may be added would comprise the following components in an aqueous medium at 30 to 80% solids:
A typical water-based ink composition to which the alkylformamide surfactants of the invention may be added would comprise the following components in an aqueous medium at 20 to 60% solids:
A typical water-based agricultural composition to which the alkylformamide surfactants of the invention may be added would comprise the following components in an aqueous medium at 0.1 to 80% ingredients: